Protein kinases belong especially to the following group: EGFR, Fak, FLK-1, FGFR1, FGFR2, FGFR3, FGFR4, FGFR5, flt-1, IGF-1R, KDR, PLK, PDGFR, tie2, VEGFR, AKT, and Raf.
Cancer remains a disease for which the existing treatments are clearly insufficient. Certain protein kinases, especially including IGF-1R (Insulin Growth Factor 1 Receptor), play an important role in many cancers. The inhibition of such protein kinases is potentially important in the chemotherapy of cancers, especially for suppressing the growth or survival of tumors.
Protein kinases participate in signaling events that control the activation, growth and differentiation of cells in response either to extracellular mediators or to changes in the environment. In general, these kinases belong to two groups: those that preferentially phosphorylate serine and/or threonine residues and those that preferentially phosphorylate tyrosine residues [S. K. Hanks and T. Hunter, FASEB. J., 1995, 9, pages 576-596]. The serine/threonine kinases are, for example, the isoforms of the protein kinases C [A. C. Newton, J. Biol. Chem., 1995, 270, pages 28495-28498] and a group of cycline-dependent kinases, for instance cdc2 [J. Pines, Trends in Biochemical Sciences, 1995, 18, pages 195-197]. The tyrosine kinases comprise growth factor receptors, for instance the epidermal growth factor (EGF) receptor [S. Iwashita and M. Kobayashi, Cellular Signalling, 1992, 4, pages 123-132], and cytosol kinases, for instance p56tck, p59fYn and ZAP-70 and the kinases csk [C. Chan et. al., Ann. Rev. Immunol., 1994, 12, pages 555-592].
Abnormally high levels of kinase protein activity have been implicated in many diseases, resulting from abnormal cellular functions. This may arise either directly or indirectly from a dysfunction in the mechanisms for controlling the kinase activity, linked, for example, to a mutation, an overexpression or an inappropriate activation of the enzyme, or an over- or underproduction of cytokines or of growth factors, also involved in the transduction of the signals upstream or downstream of the kinases. In all these cases, a selective inhibition of the action of the kinases offers hope of a beneficial effect.
The type 1 receptor for in the insulin-like growth factor (IGF-I-R) is a transmembrane receptor with tyrosine kinase activity which binds firstly to IGFI, but also to IGFII and to insulin with lower affinity. The binding of IGF1 to its receptor results in oligomerization of the receptor, the activation of tyrosine kinase, intermolecular autophosphorylation and the phosphorylation of cell substrates (main substrates: IRS1 and Shc). The receptor activated by its ligand induces mitogenic activity in normal cells. However, IGF-I-R plays an important role in “abnormal” growth.
Several clinical reports underline the important role of the IGF-I route in the development of human cancers.
IGF-I-R is often found overexpressed in many types of tumors (breast, colon, lung, sarcoma, etc.) and its presence is often associated with a more aggressive phenotype.
High concentrations of circulating IGF1 are strongly correlated with a risk of prostate cancer, lung cancer and breast cancer.
Furthermore, it has been widely documented that IGF-I-R is necessary for establishing and maintaining the transformed phenotype in vitro as in vivo [Baserga R, Exp. Cell. Res., 1999, 253, pages 1-6]. The kinase activity of IGF-I-R is essential for the transformation activity of several oncogenes: EGFR, PDGFR, the large T antigen of the SV40 virus, activated Ras, Raf, and v-Src. The expression of IGF-I-R in normal fibroblasts induces a neoplastic phenotype, which may then result in the formation of a tumor in vivo. The expression of IGF-I-R plays an important role in substrate-independent growth. IGF-I-R has also been shown to be a protector in chemotherapy-induced and radiation-induced apoptosis, and cytokine-induced apoptosis. Furthermore, the inhibition of endogenous IGF-1-R with a negative dominant, the formation of a triple helix or the expression of an antisense sequence brings about suppression of the transforming activity in vitro and reduction of tumor growth in animal models.
FAK is a cytoplasmic tyrosine kinase that plays an important role in transducing the signal transmitted by the integrins, a family of heterodimeric receptors of cellular adhesion. FAK and the integrins are colocalized in perimembrane structures known as adhesion plaques. It has been shown in many cell types that the activation of FAK and its phosphorylation on tyrosine residues and in particular its autophosphorylation on tyrosine 397 were dependent on the binding of the integrins to their extracellular ligands and thus induced during cellular adhesion [L. Komberg, et al. J. Biol. Chem. 267(33): 23439-442 (1992)]. The autophosphorylation on tyrosine 397 of FAK is a binding site for another tyrosine kinase, Src, via its SH2 domain [Schaller et al. Mol. Cell. Biol. 14: 1680-1688 1994; Xing et al. Mol. Cell. Biol. 5: 413-421 1994]. Src can then phosphorylate FAK on tyrosine 925, thus recruiting the adapter protein Grb2 and inducing in certain cells activation of the ras and MAP kinase pathway involved in controlling cellular proliferation [Schlaepfer et al. Nature; 372: 786-791 1994; Schlaepfer et al. Prog. Biophy. Mol. Biol. 71: 435-478 1999; Schlaepfer and Hunter, J. Biol. Chem. 272: 13189-13195 1997].
The activation of FAK can thus induce the jun NH2-terminal kinase (JNK) signaling pathway and result in the progression of the cells to the GI phase of the cellular cycle [Oktay et al., J. Cell. Biol. 145: 1461-1469 1999]. Phosphatidylinositol-3-OH kinase (PI3-kinase) also binds to FAK on tyrosine 397 and this interaction might be necessary for the activation of PI3-kinase [Chen and Guan, Proc. Nat. Acad. Sci. USA. 91: 10148-10152 1994; Ling et al. J. Cell. Biochem. 73: 533-544 1999]. The FAK/Src complex phosphorylates various substrates, for instance paxillin and p130CAS in fibroblasts [Vuori et al. Mol. Cell. Biol. 16: 2606-2613 1996].
The results of numerous studies support the hypothesis that FAK inhibitors might be useful in treating cancer. Studies have suggested that FAK might play an important role in in vitro cell proliferation and/or survival. For example, in CHO cells, certain authors have demonstrated that the overexpression of p125FAK induces an acceleration of the G1 to S transition, suggesting that p125FAK promotes cellular proliferation [J. -H. Zhao et al. J. Cell Biol. 143: 1997-2008 1998]. Other authors have shown that tumor cells treated with FAK antisense oligonucleotides lose their adhesion and go into apoptosis (Xu et al, Cell Growth Differ. 4: 413-418 1996). It has also been demonstrated that FAK promotes the migration of cells in vitro. Thus, fibroblasts that are deficient for the expression of FAK (“knockout” mice for FAK) show a rounded morphology and deficiencies in cell migration in response to chemotactic signals, and these defects are suppressed by reexpression of FAK [D J. Sieg et al., J. Cell Science. 112: 2677-91 1999]. The overexpression of the C-terminal domain of FAK (FRNK) blocks the stretching of adherent cells and reduces cellular migration in vitro [A. Richardson and J. T. Parsons Nature. 380: 538-540 1996]. The overexpression of FAK in CHO or COS cells or in human astrocytoma cells promotes migration of the cells. The involvement of FAK in promoting the proliferation and migration of cells in numerous cell types in vitro suggests the potential role of FAK in neoplastic processes. A recent study has effectively demonstrated the increase in the proliferation of tumor cells in vivo after induction of the expression of FAK in human astrocytoma cells [L. A. Cary et al. J. Cell Sci. 109: 1787-94 1996; D. Wang et al. J. Cell Sci. 113: 4221-4230 2000]. Furthermore, immunohistochemical studies on human biopsies have demonstrated that FAK is overexpressed in prostate cancer, breast cancer, thyroid cancer, cancer of the colon, melanoma, brain cancer and lung cancer, the level of expression of FAK being directly correlated to the tumors having the most aggressive phenotype [T M Weiner et al. Lancet. 342 (8878): 1024-1025 1993; Owens et al. Cancer Research. 55: 2752-2755 1995; K. Maung et al. Oncogene 18: 6824-6828 1999; D. Wang et al. J. Cell Sci. 113: 4221-4230 2000]. Protein kinase AKT (also known as PKB) and phosphoinositide 3-kinase (PI3K) are involved in a cell signaling pathway that transmits signals from growth factors activating membrane receptors.
This transduction pathway is involved in numerous cellular functions: regulation of apoptosis, control of transcription and translation, glucose metabolism, angiogenesis and mitochondrial integrity. First identified as an important component of insulin-dependent signaling pathways regulating metabolic responses, serine/threonine kinase AKT was then identified as a mediator playing a key role in survival induced with growth factors. It has been shown that AKT can inhibit death by apoptosis induced by various stimuli, in a certain number of cell types and tumor cells. In accordance with these findings, it has been shown that AKT can, by phosphorylation of given serine residues, inactivate BAD, GSK3β, caspase-9, and Forkhead transcription factor, and can activate IKKalpha and e-NOS. It is interesting to note that the protein BAD is found hyper-phosphorylated in 11 human tumor cell lines out of 41 studied. Furthermore, it has been shown that hypoxia modulates the induction of VEGF in cells transformed with Ha-ras by activating the PI3K/AKT pathway and by involving the binding sequence of the HIF-1 (hypoxia inducible factor-1) transcription factor known as HRE for “hypoxy-responsive element”.
AKT plays a very important role in cancer pathologies. The amplification and/or overexpression of AKT has been reported in many human tumors, for instance gastric carcinoma (amplification of AKT1), ovary carcinoma, breast carcinoma or pancreatic carcinoma (amplification and overexpression of AKT2) and breast carcinomas deficient in estrogen receptors, and also androgen-independent prostate carcinomas (overexpression of AKT3). Furthermore, AKT is constitutively activated in all the PTEN (−/−) tumors, the PTEN phosphatase being deleted or inactivated by mutations in many types of tumors, for instance carcinomas of the ovary, of the prostate, of the endometrium, glioblastomas and melanomas. AKT is also involved in the oncogenic activation of bcr-abl (references: A. Khawaja, Nature 1999, 401, 33-34; Cardone et al. Nature 1998, 282, 1318-1321; S. Kitada et al., Am. J. Pathol. 1998 January; 152(1): 51-61; N M Mazure et al. Blood 1997, 90, 3322-3331; H. Zhong et al. Cancer Res. 2000, 60, 1541-1545).